A drunken, off-duty Manhattan cop who pulled his service weapon on an Inwood school teacher in a random attack last August was found guilty of three counts of predatory sexual assault carrying a potential maximum sentence of life in prison, a jury said this afternoon in issuing a partial verdict in the case.

Pena was additionally convicted of violating the woman during the heinous attack on the woman, a stranger to him who had been on her way to her first day of teaching second grade when the cop pulled her into a backyard and threatened to shoot her in the face.

After four days of what jurors described in a note as sometimes contentious deliberations, the Manhattan Supreme Court panel was unable to come to a unanimous verdict on two counts of rape and two counts of predatory sexual assault connected to the two rape charges.

A few hours after the verdict, the NYPD fired Pena.

The petite, brunette victim — who was only 25 years old when Pena held a gun to her head and attacked her in an Inwood backyard last August — sobbed quietly as she sat in the second row of the courtroom waiting to hear the partial verdict.

She burst into audible, gasping sobs at one point — when the jury forewoman said that the jury was unable to come to a verdict on the predatory sexual assault charges connected to the alleged rape.

Earlier in the day, deliberations came to a halt when it emerged that Juror No. 2 gave a campaign contribution to DA Cy Vance and worked for former “love guv” Eliot Spitzer.

Prosecutors revealed that the panelist is lawyer Lloyd E. Constantine, a former advisor Spitzer.

Constantine, one of four attorneys on the panel, is also a law partner of Richard Aborn, who ran against Vance. Juror No. 2 gave $5,000 to both Vance and Aborn in 2008.

During voir dire, Constantine and other jurors were asked if they had a connection to the DAs office or police and he said, “No.”

Constantine — whose leanings either way in the case are unknown — was called into court and on the carpet shortly before the lunch break, and assured the trial judge that he remains objective despite his pro- and anti-DA ties.

Constantine also penned a book on the Spitzer ordeal called, ”Journal of the Plague Year.”

The political insider said he didn’t inform the judge of these ties during jury selection because “I had already passed my own subjective test” of objectivity, and didn’t want anyone to think he was trying to get out of jury duty, he said.

As one of the governor’s most trusted aides, Constantine was quoted frequently in the press during Spizter’s political crash and burn. The governor and his wife Silda reportedly fumed over Constantine’s willingness to talk on the record, leading to a huge strain in their once-close relationship.

Constantine was allowed to continue deliberations.

“They said there’s a lot of anger going on — a lot of ad hominum attacks,” Pena’s defense lawyer Ephraim Savitt told reporters, speaking of a note that was not immediately read into the record.

“And they don’t think it’s going to get any better.”

Jurors had first told the judge of an “impasse” yesterday. They have reached a verdict on six other sex attack charges in the case, they also told the judge yesterday, which were not revealed until today.

Yesterday, the 25-year-old victim, a petite, bespectacled brunette sobbed softly in a courthouse hallway when lead prosecutor Evan Krutoy told her of the lack of agreement on the rape count.

The victim had insisted in emotional testimony that she was certain she was raped. “It hurt,” she explained tearfully of her certainty.

Defense lawyer Savitt has told jurors that Pena admits pulling his service weapon on the terrified woman, a total stranger who was on route to her first day of school, and to sexually attacking her in a random Inwood backyard. But he has argued that there are no direct forensics confirming that there was actual intercourse.

But one passerby testified that, from 12 feet away, it appeared that Pena was having intercourse with the woman. Forensic exams found the woman’s DNA on Pena’s genitals and Pena’s DNA on the woman’s underwear.